The present invention relates to magneto-optical disks, magneto-optical tapes, magneto-optical card, and other similar magneto-optical storage media for use with magneto-optical recording/reproduction devices and methods of reproducing the same.
Conventionally, magneto-optical disks incorporating magneto-optical storage media have found commercial applications as rewritable optical storage media. The magneto-optical disk records/erases data through heating of a part of the magneto-optical storage medium by focusing a light beam emitted from a semiconductor laser device on the magneto-optical storage medium. The recorded data is reproduced by projecting a focused light beam on the magneto-optical storage medium with such intensity that causes no data erasure and then identifying the polarization of the reflected light.
Such a magneto-optical storage medium has a problem that reproduction characteristics degrade when the spot diameter of the light beam is relatively large compared with the diameter and interval of the recording bits in the magnetic domain where data is recorded. This is because the light beam, although being focused on the target recordings bit, forms a relatively large spot encompassing those recording bits immediately adjacent to the target bit, and thus fails to distinguish between the recording bits in reproduction.
Japanese Laid-Open Patent Application Nos. 9-320134/1997 (Tokukaihei 9-320134 published on Dec. 12, 1997, corresponding to U.S. Pat. No. 5,939,187) and Japanese Laid-Open Patent Application No. 10-049926/1998 (Tokukaihei 10-049926 published on Feb. 20, 1998, corresponding to U.S. Pat. No. 5,955,191) discloses magneto-optical storage Media addressing the foregoing problem. In the former patent application, the suggested magneto-optical storage medium includes: a reproduction magnetic layer exhibiting in-plane magnetization at room temperature and perpendicular magnetization at temperatures at or higher than a critical temperature; an in-plane magnetized film with a Curie temperature in the proximity of the critical temperature; a non-magnetic intermediate layer; and a recording magnetic layer constituted by a perpendicularly magnetized film where information is recorded. In the latter patent application, the suggested magneto-optical storage medium includes: a reproduction magnetic layer constituted by a perpendicularly magnetized film; an in-plane magnetized layer; a reproduction magnetic layer constituted by a perpendicularly magnetized film; another in-plane magnetized layer; and a recording magnetic layer constituted by a perpendicularly magnetized film where information is recorded.
In these magneto-optical storage media, the reproduction magnetic layer exhibits in-plane magnetization at temperatures not higher than a critical temperature or at temperatures not higher than the Curie temperature of the in-plane magnetized layer; therefore, the information recorded in a recording magnetic domain of a recording magnetic layer is not copied to the reproduction layer, rendering the information in the recording magnetic domain unreproducible. By contrast, the reproduction magnetic layer exhibits perpendicular magnetization at temperatures not lower than a critical temperature or at temperatures not lower than the Curie temperature of the in-plane magnetized layer; therefore, the information recorded in a recording magnetic domain of the recording magnetic layer is copied to the reproduction magnetic layer, allowing the information in the recording magnetic domain to be reproduced. For these reasons, individual recording bits can be distinguished from one another in reproduction, enabling the reproduction of information recorded with high density, if the reproduction power of the light beam and the critical temperature at which the reproduction magnetic layer changes to perpendicular magnetization are appropriately specified, even when the light beam focused on the reproduction magnetic layer forms a beam spot encompassing adjacent recording bits.
Nevertheless, in recent years, optical disks are required to improve their storage capacity further. Accordingly, the magneto-optical storage media disclosed in Japanese Laid-Open Patent Application No. 9-320134/1997 (Tokukaihei 9-320134) and Japanese Laid-Open Patent Application No. 10-049926/1998 (Tokukaihei 10-049926) mentioned above come short of providing sufficient masking effect of in-plane magnetization and sufficient reproduction resolution.
The present invention has an object to offer magneto-optical storage media that can improve masking effect of in-plane magnetization and also to offer a method of reproducing the same.
In order to achieve the above object, a magneto-optical storage medium in accordance with the present invention is characterized in that
it includes:
a reproduction magnetic layer exhibiting in-plane magnetization at room temperature and changing to perpendicular magnetization at a critical temperature or higher;
a plurality of in-plane magnetized layers with Curie temperatures in a; proximity of the critical temperature and opposite magnetic polarities between every adjacent pair of the plurality of in-plane magnetized layers; and
a recording magnetic layer fabricated from a perpendicularly magnetized film,
the reproduction magnetic layer, the plurality of in-plane magnetized layers, and the recording magnetic layer being sequentially deposited,
wherein the reproduction magnetic layer is exchange-coupled with the plurality of in-plane magnetized layers at least at room Temperature.
With the arrangement, the exchange coupling between the plurality of in-plane magnetized layers with opposite magnetic polarities forms an inter-surface magnetic wall; this greatly enhances ability to retain the in-plane magnetization against magnetic flux leakage. In this manner, the arrangement retains the in-plane magnetization of the reproduction magnetic layer and reinforces in-plane magnetization masking, resulting in improvement in reproduction resolution.
As in the foregoing, the present invention successfully improves masking effect of the in-plane magnetized layers and also reproduces signals with sufficient quality from recording bits of small diameters and intervals, i.e., improves reproduction resolution in magnetic super-high resolution reproduction.
In order to achieve the above object, another magneto-optical storage medium in accordance with the present invention is characterized in that
it includes:
a reproduction magnetic layer exhibiting perpendicular magnetization from room temperature to a Curie temperature when used alone;
a plurality of in-plane magnetized layers with Curie temperatures lower than the Curie temperature of the reproduction magnetic layer and opposite magnetic polarities between every adjacent pair of the plurality of in-plane magnetized layers; and
a recording magnetic layer fabricated from a perpendicularly magnetized film,
the reproduction magnetic layer, the plurality of in-plane magnetized layers, and the recording magnetic layer being sequentially deposited,
wherein the Reproduction magnetic layer is exchange-coupled with the plurality of in-plane magnetized layers and thereby exhibits in-plane magnetization at least at room temperature.
With the arrangement, the exchange coupling of the reproduction magnetic layer fabricated from a perpendicularly magnetized film with the plurality of in-plane magnetized layers with Curie temperatures lower than the Curie temperature of the reproduction magnetic layer aligns the magnetization of the reproduction magnetic layer in parallel to the in-plane direction and thus causes the reproduction magnetic layer to exhibit in-plane magnetization at temperatures not higher than the Curie temperatures of the plurality of in-plane magnetized layers. Consequently, in-plane magnetization masking is provided to the reproduction magnetic layer similarly to the; above arrangement, enabling magnetic super-high resolution reproduction.
In order to achieve the above object, a method of reproducing information on a magneto-optical storage medium in accordance with the present invention is characterized in that
the magneto-optical storage medium includes:
a reproduction magnetic layer exhibiting in-plane magnetization at room temperature and changing to perpendicular magnetization at a critical temperature or higher;
a plurality of in-plane magnetized layers with Curie temperatures in a proximity of the critical temperature and opposite magnetic polarities between every adjacent pair of the plurality of in-plane magnetized layers; and
a recording magnetic layer fabricated from a perpendicularly magnetized film,
the reproduction magnetic layer, the plurality of in-plane magnetized layers, and the recording magnetic layer being sequentially deposited,
wherein the reproduction magnetic layer is exchange-coupled with the plurality of in-plane magnetized layers at least at room temperature, and also in that
the method includes a step of heating the reproduction magnetic layer and the plurality of in-plane magnetized layers to or exceeding the proximity of the critical temperature.
In order to achieve the above object, another method of reproducing information on a magneto-optical storage medium in accordance with the present invention is characterized in that
the magneto-optical storage medium includes:
a reproduction magnetic layer exhibiting perpendicular magnetization from room temperature to a Curie temperature when used alone;
a plurality of in-plane magnetized layers with Curie temperatures lower than the Curie temperature of the reproduction magnetic layer and opposite magnetic polarities between every adjacent pair of the plurality of in-plane magnetized layers; and
a recording magnetic layer fabricated from a perpendicularly magnetized film,
the reproduction magnetic layer, the plurality of in-plane magnetized layers, and the recording magnetic layer being sequentially deposited,
wherein the reproduction magnetic layer is exchange-coupled with the plurality of in-plane magnetized layers and thereby exhibits in-plane magnetization at least at room temperature, and also in that
the method includes a step of heating the reproduction magnetic layer and the plurality of in-plane magnetized layers to or exceeding the Curie temperatures of the plurality of in-plane magnetized layers.